build(aio): change examples to CLI (#19248)

PR Close #19248

aio/content/examples/forms/src/app/app.component.ts

@@ -2,7 +2,7 @@
 import { Component } from '@angular/core';
 
 @Component({
-  selector: 'my-app',
-  template: '<hero-form></hero-form>'
+  selector: 'app-root',
+  template: '<app-hero-form></app-hero-form>'
 })
 export class AppComponent { }

aio/content/examples/forms/src/app/hero-form.component.ts

@@ -5,7 +5,7 @@ import { Component } from '@angular/core';
 import { Hero }    from './hero';
 
 @Component({
-  selector: 'hero-form',
+  selector: 'app-hero-form',
   templateUrl: './hero-form.component.html'
 })
 export class HeroFormComponent {